Motor drive system for motionpicture equipment



Nov. 3, 1953 J. PETTUS 2,657,870

MOTOR DRIVE SYSTEM FOR MOTION-PICTURE EQUIPMENT Filed Oct. 31, 1950 I 2 Sheets-Sheet 1 70 367/302 C 61 a MWAWJI/PPLY mmvroa J /mss L. PEITUS,

w/fwfz Nov. 3, 1953 J. PETTUS 2,657,870

MOTOR DRIVE SYSTEM FOR MOTION-PICTURE EQUIPMENT Filed Oct. 31, 1950 2 Sheets-Sheet 2 I 7'0 i BI /709:5 1 POMS? MI INVENTOR.

Jams A. P152705 fll' r GENE Y Patented Nov. 3, 1953 r MOTOR DRIVE SYSTEM-FOB MOTION CT RE Q IPM N James Ldettua-Enelno, CalihyassignoftoRadio Corporation of America, a--:corporotion ol 1 Delaware Application. octobe 31, 1950,.sma1N....193,1o9

This invention relates to electricalmotorzdrlve systems,v and particularly to a plural motordrive system for motion picturesoun'd film recorders.

In. the advancement of motion picture. film, either with pictures. only,.. sound only, or with both pictures and sound, electrical motors are used for advancingthe film through the. specific apparatus, such asasound projector, sound recorder,..and soundreproducer', The film used is usually on reels or in rolls, and'is fed from a supply reeltc a takeupreel. These reels are generally. enclosed in magazines, particularly if the apparatus is a. soundrecorder; The apparatus usually employs a sprocket for advancing the film, the film passing .overa filter roller in order to. provide itwithuniformly. constant speed at the sound translation point. :Thisconstant speed is subject to variations which. may .come from the film. supplyandtakeup; reels... For instance, the film may-feed off the supply reel jerks, so usually a drag of someform used to maintaina substantially-constant tension in the fi1m-at thispoint.

It valsobecomes desirable at times to reverse the film without removing the reels. or' rolls, particularly in sound film .reproducers. .Th present invention permits this to beaccomplished in.a verysimple and rapid manner. .Another feature of. the invention is. that the film is easily threaded and the reel motor system .is easily connected into the power supply ofthe main film drive motor.

--The-invention includes three mutually, electrically controlled motors, one for the film sprocket, and one for each of the film reels, Themotors are .mechnically independent, so they independentlydrive their respective .loads .ormaintain the necessary. tension in the film so that no slack occurs: in the film path atany-time.

The principal object of the invention, therefore'is'to facilitate the ieeding or. advancement of film from .and to supply reels through film systems.

Another; object of theinvention is to supply an improved film magazine drive and, controls therefor.

Aiurtherobject of theinventionisto provide animproved film drive motor system-which aids in threading the film,. the advancement of the film, and: the rewinding of the film. -A-still further object. of theinventionis to pro-.- vide an improved motor drive formation-picture equipment.

Although the novel-features which are believed to cha a e stic o this invention will .be

' 9ClaIm's; (01142-55) pointed. out with particularity in the appended claims, the manner 01' itsorganization and the modeoi' its operation'will be betterunderstood by referring to the rollcwing descriptiomwread in conjunctionwith the accompanying drawings, forming a part hereof,.in which: l is'aplan .viewof the invention embodied n a sound film. recorder.

Fig. 2 is an elevational s own n ig. 1.

; Fi 3, is a schematic circuit diagram 01" one embodiment of the control circuits, and

Fig. 4 is a schematic circuitdiagram of another embodiment of the control circuits.

"Referringnow to the drawings, in which the same numerals identify like elements, aselfsynchronous type offimotor 5 drives a main film sprocket .G usually through a reduction. gear box, notshown. .Afilm J is shown being supplied from a; roll 8 on areel 9 to the left-hand .side of sprocket .6 under rollers ll around a tensioningand guide roller 12,- around a drum 13,.which usually film-pulled, I around .a tensioning. and guide roller [Land over theIright-hand end of the sprocketli under" rollers l5, fromwhich it goes ,to .aroll all ,on a reel "3.. For purposes of illustration, an .opticaliunit is diagrammatically illustrated at 20.. Q'Iheireels 9 and [8. are shown in ama'gazineji on afilm sound recorder 26. In ,Fig..1,.single phase induction motorshaving high resistance rotors, and commonly known astorquemotors, are shown-at 2 l and 22. :Motor 2|..is directlyconnected-by a shaft ,23 to thehub oi the reel 9,.and motor 22is directly connected by a shaft .24 tothe hub, of. reel l8.-. No slipping clutches,.-pulleys, belts, or chains are used. As mentioned. above, motor, 5 is of theself-synchronous type, .sothatit my be lockedinposi-r tionatstandstill with .other similarmotors, and then acceleratedin step. with. similar motors. A three-phase..synchrcnous motor v could also be l d- Referring now to Fig. 3, the motor 5 is shown with only a three-phase. stator winding, it being understood. that-a. self-synchronous motor h s a three-phase rotor winding interconnected with the rotorsqof. similar motors to be driven'in synohronism. ,The statoriis connected over conductors 28, 29,. and 30.to,any..suitab1e three-phase DOWer .-supp1y-.=over switches 32 and 33-,;.1.Thus. when. switch 3Z;..,ls-;closed, single phasesenergy is'supplied .towmotort to lock-it upandewhen switch .33visvclosed; threeephase energy is suppliedqto start and run themotor.

.z when'switch 32zis closed,'single:phase energy view of the system is also supplied to motors 2| and 22 over resistors 35 and 36, conductors 31 to 44, inclusive, and switch contacts 45 and 45. The motors 2| and 22 are shown with starting condensers 49 and 50. The circuits just traced energize the motors 2| and 22 at approximately twenty-five percent of their rated value for normal operation. Under these conditions, a low value of torque is created, but sufiicient to take up the slack in film I. The motors remain stalled and the film stopped and taut. Because of the inherent design of these motors, they may withstand this condition without damage. Each motor is connected to run in the same direction, this direction being counterclockwise in Fig. 2.

Now, when switch 33 is closed, the motor 5 is started, relay 52 is energized over conductors 34 and 53, and the resistors 35 and 35 are shortcircuited by switches 55 and 55 making their right-hand contacts. This supplies normal torque to motors 2| and 22 sufiicient for motor 22 to wind the film on reel l8 as it is advanced thereto by sprocket 6 driven by motor 5. Motor 2|, however, provides a holdback tension on the film to aid in obtaining uniform film motion at drum l3.

To stop the system, switch 33 is first opened, which allows motors 2| and 22 to take up slack at reduced torque, since relay 52 is now de-energized and resistors 35 and 35 are back in the energizing circuits of these motors. As it takes the recording mechanism a longer time to coast to a stop because of its greater inertia, the motors 2| and 22 maintain the film taut during this time period. Switch 32 is next opened, and the system becomes neutral. The closing of switch 53 energizes a relay 59, which switches conductors 4| and 42 to the other sides of condensers 49 and 50 to reverse the motors, the film then feeding onto reel 9 from underneath and ofi of reel Hi from the top. When the sprocket 5 is reversed, motor 2| will wind the film on roll 3 and motor 22 provides the holdback tension.

Motors 2| and 22 have twelve poles to provide a synchronous no-load speed of 600 revolutions per minute at sixty cycles. This provides overdrive to the reels having a ratio varying between 600/350 and 600/50 revolutions per minute approximately for minimum and maximum speed, respectively, of a reel having a hub diameter of two inches and a film speed of ninety feet per minute.

In Fig. 4, a simplified circuit is shown when the motor 5 is of the self-synchronous type with three-phase Y-connected windings, as shown. This circuit shows the three-phase power supply connected to switches 6| and 52, and the windings of motor 5 connected over conductors 53. 54, and 55. Resistor 51 and resistor 55 may be previously set to provide the desired normal operating voltage for each of motors 2| and 22. Reversing switches are shown at 10 and 1 l, which may be interconnected and operated by hand or by relay, as in Fig. 3.

The system of Fig. 4 is operatedin the same manner as that of Fig. 3. That is, switch 5| is first closed, which locks up motor 5. The motors 2| and 22 are also energized over conductors 54, I2, I3, 14, and I5, and the stator windings of motor 5. The normal line voltage may be 230 volts, but the circuit just traced would apply approximately 115 volts to the motors 2| and 22 because of the voltage drop in the stator windings. This voltage is then reduced to approximately '15 volts by resistors 51 and 53, which provides the desired standstill torque to take up film slack.

Now, when switch 52 is closed, motor 5 is started and full voltage is supplied to motors 2| and 22 over conductors 54, I2, I3, 14, and 15 only. The system then operates the same as described above. The supply reel motor provides the holdback tension, and the takeup reel motor takes up the film, the differential being supplied by the film drive motor 5.

I claim:

1. A plural film drive motor control system comprising a first motor, means for advancing a film with said motor, a pair of motors, means for winding said film with one of said motors, means for introducing tension in said film with the other of said pair of motors, means for partially energizing all or said motors simultaneously to tension said film at,standstill, and means for normally energizing all of said motors simultaneously for advancing said film, said first motor advancing said film to said winding means and pulling said film against the tension introduced by said other of said pair of motors.

2. A plural film drive motor control system in accordance with claim 1. in which said winding film means is a film takeup reel directly connected to said first mentioned motor of said pair and said tensioning means is a film supply reel directly connected to said other motor of said pair, said other motor tending to hold back said film as it is advanced by said first mentioned means.

3. A plural film drive motor control system in accordance with claim 1. in which said first motor is a three-phase self-synchronous motor and said pair of motors are single phase induction motors having high resistance rotors.

4. A control circuit for a film advancing motor and a pair of film reel motors comprising a threephase power supply, a first switch for supplying power from one phase of said supply to all of said motors to partially energize said film advancing motor, means in the circuit between said one phase of said power supply and said pair of motors for limiting the energy to and par tially energizing said pair of motors to tension said film, a second switch for connecting the other phases of said three-phase power supply to said film advancing motor, and means connected to said power supply through said second switch for eliminating said energy limiting means from said circuit when three-phase power is supplied to said film advancing motor.

5. A control circuit in accordance with claim 4, in which said energy limiting means are resistors in said circuit, and said eliminating means is a relay connected to said power supply for shortcircuiting said resistors when said three-phase power is supplied to said film advancing motor.

6. A control circuit in accordance with claim 4. in which motor reversing switches are provided in said circuit to said pair of motors and a relay energized by said power supply is provided for actuating said motor reversing switches.

7. A film magazine reel drive comprising a pair of torque motors, a film supply reel, a film takeup reel, means for directly connecting one of said motors to said supply reel, means for directly connecting the other of said motors to said takeup reel, a film advancing sprocket, a motor connected to said sprocket, a film threaded from said supply reel over said sprocket to said takeup reel, and means for partially energizing said torque motors for tensioning said film at standstill, said means including the stator windings of said sprocket motor.

8. A power control system for a self-synchrofilm advancing sprocket and one of said pair of motors being connected to a film supply reel and the other of said pair of motors being connected to a film takeup reel, comprising a three-phase power supply, a first switch, a circuit for connecting one phase of said power supply to said self-synchronous motor to lock said motor and to said pair of motors through the windings of said self-synchronous motor, a second switch for connecting the three phases of said power supply to said self-synchronous motor, and a circuit for directly connecting said pair of motors to one phase of said power supply.

9. A power control system in accordance with claim 8, in which a pair of switches are provided 5 for reversing said pair of motors.

JAMES L. PETTUS.

References Cited in the file of this patent UNITED STATES PATENTS 

